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[From the Puoceedings of the Royal Society, A, Vol. 98, 1920. J 



OBERLIN COLLEGE 

Laboratory Bulletin No. 36 

The Magnetic Mechanical Analysis of Manganese Steel. 

By Sir EGBERT HADFIELD, F.B.S., and Messrs. S. E. 
WILLIAMS AND I. S. BOWEN. 






OBERLIN 

1920 



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[Reprinted from the Proceedings of the Royal Society, A. Vol. 98] 



The Magnetic Mechanical Analysis of Manganese Steel. 

By Sir Egbert Hadfield, F.R.S., and Messrs. S. K Williams and I. S. Bowejt, 
of the Department of Physics, Oberlin College, Oberlin, Ohio, U.S.A. 

(Received December 10, 1920.) 

One of the most interesting alloys for the study of its magnetic properties 
is manganese steel. The following paper is an attempt to correlate some of 
the magnetic and mechanical properties of manganese steel, in the hope that 
as such data are circulated it will eventually be possible to interpret from the 
magnetic behaviour of steel what the mechanical properties will be. 

Six manganese steel rods supplied by one of the authors were drawn from 
the same source, 76 cm. long and 0*95 cm. in diameter, and used " as drawn." 
These rods were marked 1, 2, 3, 4, 5, and 6 respectively. The chemical 
analysis was made on rod No. 4 and showed : — 

C 1'25 per cent. 

Si 0-43 

Mn 12-20 

The record for the heat treatment was as follows : — " All six bars were 
treated at 1000° C. (five minutes), and then water-quenched in ordinary cold 
water. Nos. 1, 5 and 6 were then enclosed in an iron pipe welded over at the 
ends, and annealed. The time for cooling from 550° C. to 450° C. was about 
eight hours. As this treatment did not make the bars sufficiently magnetic 
they were again annealed at 500° C. (530° 0.-475° C.) for sixty hours." 

Rough tests were made on the rods (without removing outer skin) with 
balanced hand magnet. Rods Nos. 2, 3 and 4, were non-magnetic ; hand magnet 
just pulled at 1/16 inch. Rods 1, 5 and 6 were magnetic; hand magnet 
pulled well at 3/8 inch. About 25 per cent. Sp. Mag. (S.C.I. — Swedish 
Charcoal Iron = 100). From these six rods Nos. 2 and 5 were selected to 
represent the non-magnetic and magnetic types respectively, one differing 
from the other only in heat treatment. 

These rods were used to study the changes in length which occur when a 
ferro-magnetic substance is subjected to a magnetic field, as well as the effects 
upon the values of the intensity of magnetisation when the rods are subjected 
to a longitudinal stress. It would appear, therefore, that more and more is it 
going to be possible* to determine what will be the mechanical properties of 

* Burrows, * Sci. Paper, No. 272, Bur. Stands.' ; Williams, ' Jour. Cleveland Eng. Soc.,' 
January, 1917 ; ' Topical Discussion on Magnetic Analysis, A.S.T.M.,' June Meeting, 
1919; Gebert, 'Jour. A.S.T.S.,' June, 1919; Sanford and Kouwenhoven, 'Sci. Paper, 
No. 343, Bur. Stands.' 

b 



298 Sir R. Hadfield, Messrs. S. R Williams, and T. S. Bowen, 

ferro-magnetic substances by a study of their magnetic behaviour. In the two 
relations which are to be studied in this paper we have an excellent avenue 
of approach to this fascinating subject. 

The method* devised by one of iis for determining the Joule effect (length 
changes), was employed in this work. The length of rods between brass 
extensions was 74-3 cm. In fig. 1 is shown the variations in length of rod, 
No. 5, as the magnetic field was increased from zero up to nearly 3000 Gauss. 
This shows that for all field strengths used, the change in length was an 
increment. In a similar way rod No. 2 was tried out but no changes in 
length could be detected, although changes as small as 0'000004 cm. could be 
read from the scale. 

Working in the same vertical solenoid as used in the Joule effect, the rods 
were next tested for the effect of tension on the intensity of magnetisation 
(Villari effect). In the usual ballistic method for the measurement of the 
intensity of magnetisation of rods a small coil of wire is wound about the 
middle section of the specimen and the terminals of this exploring coil 
attached to a ballistic galvanometer. The rod thus equipped is placed in a 
long solenoid, to ensure as nearly as possible a uniform magnetic field. The 
throw of the galvanometer is then observed when the current is broken and 
reversed in the large solenoid. When this is done the charge flowing through 
the galvanometer is 

xi 

where n and ?ii are the radius and number of turns of wire respectively in 
the small exploring coil on the rod, r^ the radius of the rod to be tested, 
R the resistance of the galvanometer and exploring coil circuit, H the field 
in the solenoid, and I the intensity of the magnetisation. 

It will be seen from equation (1) that the deflection of the galvanometer 
depends on two main factors : the field of the solenoid and the flux induced 
in the rod. If the intensity factor happens to be small and H large, it will 
be hard to measure I with accuracy, as the deflection of the galvanometer 
due to it is only a very small fraction of the total reflection. 

For the so-called non-magnetic rod No. 2 it was evident that there was 
some magnetic induction, otherwise the hand magnet would not have pulled 
at any distance, no matter how small ; consequently, to measure the intensity 
of magnetisation in rod No. 2, especial care had to be used to emphasise the 
intensity of magnetisation factor in equation (1). This is accomplished 
in the following way : a second coil, having about twice the cross-section of 

* Williams, ' Phys. Rev.,' vol. 32, p. 281, March, 1911 ; vol. 34, p. 258, April, 1912 ; 
' Amer. Jour. Sci.,' vol. 36, p. 555, November, 1913. 



L 



The Magnetic Mechaidcal Analysis of Manganese Steel. 299 

the first exploring coil, but containing only about halt" as many turns, is 
placed over and concentric with the first exploring coil. The two coils are 
then connected in series with the ballistic galvanometer, so that, when the 
field, H, in the solenoid is varied, the E.M.F. generated in the first coil will 
just balance that in the second. When this is accomplished, we have the 
charge flowing through the galvanometer, 

where rs and 712 are the radius and number of turns in the outer exploring 
coil. If, now, the manganese steel rod is thrust through all of the coils, the 
charge passing through the galvanometer, when the current is broken and 
reversed in the main solenoid, is 

^-A ^ ■, {6) 

whence from (2) and (3) 

R 

i.e., since 6, the deflection of the galvanometer is proportional to Q, we can 

at once write, 

e = kL (5) 

If k can be determined, we have an absolute method* for the determination 
of I, which is workable when I is comparatively small. For the determina- 
tion of k, the following method was employed : a long slender solenoid of 
radius r^, whose general dimensions were those of the rods tested, was made 
up and used in place of the rods. When the current in this slim solenoid 
was broken and reversed, a flux was produced in the two coils connected to 
the galvanometer and the charge, 

Q^2^r4^H0H-».)_ (6) 

Here H = 4:7rnsi, where n-s is the number of terms per centimetre in the slim 
solenoid, and i the current flowing through it, hence (6) becomes 

If we exchange the rod for the coil, and vice versa, the deflections will be 

e,:e = . ~ , (8) 

* It is to be noted that this deduction holds only for infinitely long solenoids and rods. 
It is assumed in this work that the ratio of length to radius is sufiiciently large to make 
any errors due to demagnetisation eifects negligible. 

b 2 



300 Sir R Hadfield, Messrs. S. K Williams, and I. S. Bowen. 



whence solving for I we get 



I = ^1^'. (9) 



In making the double coil which was connected to the galv^anometer, 
wooden spools were used, the smaller one being just the size to fit into the 
larger one. The inner spool was wound with 1034 turns of 'No. 36 silk- 
covered wire, while the outer one had 520 turns of Xo. 28, the difference in 
size of wire making the coils about the same length. After carefully 
balancing the two coils against each other, they were fastened together 
firmly by boiling in beeswax and allowing the wax to harden between them. 
For the final adjustment, a coil of some twenty turns was wound on a spool 
which could be rotated so as to include more or less lines of force from the 
main solenoid. With this small coil in series with the double coil, an exact 
balance between the coils could be established. The balance was tested for 
field strengths up to 2000 Gauss, and no observable deflection of the 
galvanometer was present. In all of the circuits connecting these coils, it 
was very necessary to keep the wires leading to and away from the coils 
wound together, in order to avoid induction effects as much as possible. 

In determining the effects of tension on the two manganese steel rods, 
coils of several hundred turns were wound directly on the rods. These coils 
were connected to a ballistic galvanometer, and the deflections observed 
when the current through the main solenoid was broken and immediately 
reversed, first without and then with a tension of 350 kgrm. on the rod. 
From the ratio of the two deflections and the values of I, as determined 
above, the per cent, and actual change in I were calculated. 

Curve 1, fig. 2, shows the values of I for corresponding values of H in rod 
No. 5. These values are for the rod when not under tension. Curve 2, fig. 2, 
is a plot of the difference between intensity of magnetisation when under 
tension and when relieved of it. It will be seen that, for all field strengths, 
so far as we were able to go, the application of a tension increased the 
intensity of magnetisation. This is in harmony with the results shown in 
fig. 1, where the change in length was an increment for all fields. If a 
Villari reversal point had occurred, curve 2, fig. 2, would have crossed the 
axis for H, and the point of intersection would be the Villari critical point 
for the specimen of steel under investigation. 

Eod No. 2 did not show any change in intensity of magnetisation by being 
stretched, just as it did not show any change in length in a magnetic field. 
Fig. 3 shows the value of I for rod No. 2. It will be noted that I is plotted 
to a scale thirty-five times- as great as for rod No. 5 in fig. 2. A striking 
similarity between the two curves is shown when they are superimposed one 



The Magnetic Mechanical Analysis of Manganese Steel. 301 



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302 The Magnetic Mechanical Analysis of Manganese Steel, 

on the other. A factor of 36 instead of 35 would have made them ahnost 
exactly coincident. 

It was thought probable this might be due to slight oxidation and 
alteration in composition of the surface of the bar, which can only be 
avoided in heat treatment by observing special precautions not taken in the 
present instance. 

As pointed out, bars Nos. 2, 3, and 4 showed a very slight attraction with 
the hand magnet. 

It was therefore decided to remove a few thousandths of an inch from the 
surface of bar N"o. 4 by means of emery cloth. The hand magnet was then 
applied to this bar, which did not show any magnetic susceptibility. The 
slight magnetic qualities noticed in bar No. 2 in fig. 3 were therefore entirely 
due to the condition of the surface material. 

It should be added here that manganese steel is very readily oxidised, 
and consequently bars of it, unless carefully ground, are liable to what is 
termed '•' skin " trouble, that is, slight magnetic susceptibility. This arises 
from the temperatures employed in the heat treatment of this material, a 
very thin layer indeed being formed on the outer surface of the bar of 
oxidised material, which is slightly magnetic. 

In the Joule phenomenon of magnetic lengthening, we have a very definite 
mechanical effect due to a magnetic field. In the Villari effect, we have, as 
the result of a mechanical pull, a very definite change in the magnetic 
properties of the steel. These are reciprocal relations, and furnish a method 
for magnetic-mechanical analysis. Whether we shall ever be able to 
interpret all of the mechanical properties of ferromagnetic substances from 
their magnetic behaviour is a question, but from what has been accom- 
plished there are fair promises, and no avenue seems more inviting than the 
one which has been followed in this study, where the magnetic and mechanical 
effects are so closely associated. Here is a splendid opportunity for co-opera- 
tion between the large steel industries with their resources of materials, and 
the research laboratories with their resources of skilled investigators, to 
make a very thorough study of this field. X-ray methods, and the methods 
indicated above, seem to be about all the means we have at present to test 
the mechanical properties of a substance without injuring the sample tested. 
There are some advantages in the magnetic method. 



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